The present invention related to an ink container containing an absorbent member for holding the ink to be supplied to an ink jet head employed by an ink jet printer, or the like. In particular, it relates to an ink container improved to make it possible to satisfactorily use pigment-based ink.
An ink container for supplying an inkjet head with ink is structured so that the ink holding force of an ink holding member disposed in the ink container is used for generating the ink supplying pressure necessary for the ink ejection characteristic of an inkjet head, or that the pressure generated by the pressure head difference between the position of the ink surface in the ink container and the position of the ejection orifice of an inkjet head is used as the pressure for supplying ink through an ink supplying tube.
In recent years, a personal computer has come to be widely used, and with the widespread usage of a personal computer, a printer has come to be widely used. There is a call for reducing printer size, and therefore, a large number of printers employ an ink container having the former of the above described structures, in which the ink holding force of the ink holding member is utilized. As for the material for the ink holding member placed in an ink container, generally, foamed polyurethane or PP fibers are employed in consideration of ink holding member cost, and of the state of contact between the ink holding member and ink. Numerous microscopic holes or microscopic gaps in these materials generate capillary force, which functions as ink holding force. In consideration of color development, ejection stability, countermeasure for the problem that while an ink container is left unused for a long period of time, the ink in the portion of the ink absorbent member adjacent to the ink outlet dries and solidifies, and the like, dyestuff-based ink has long been used as the ink to be filled into an ink holding member structured as described above.
In recent years, even a print produced by an inkjet has begun be required to match a print produced by a laser beam printer (LBP) in terms of print density, color development, and/or resistance to ambient elements. In particular, it is desired that black ink is improved in terms of the optical density of a print produced by recording letters on ordinary recording paper.
When using an ink employing dyestuff as coloring agent, it is difficult to improve the above described optical density, because of the characteristics of dyestuff. Further, an ink employing dyestuff as coloring agent has not been improved enough to be satisfactory in terms of waterproofing and light-proofing. Thus, in order to solve the above described problems of dyestuff-based ink, it has been proposed to use recording paper dedicated for inkjet recording, more specifically, ordinary recording paper provided with an ink catching layer (coated paper). However, such recording paper is most costly than ordinary recording paper. Therefore, there has been demand for a method for improving image quality while using inexpensive ordinary recording paper.
There are some methods for effecting a high level of image quality on the surface of recording paper, in which ink density is improved by ejecting ink processing agent at the same time as ink is ejected. However, employment of any of such methods increases the size of a recording apparatus itself, and also, the cost of the ink processing agent adds to the overall cost. Thus, usage of a recording apparatus employing such a method has been limited to special jobs.
Thus, it has been proposed to use pigment as the coloring agent for ink. When pigment is used as the coloring agent for ink, it is relatively easy to increase the optical density because of the pigment properties. Further, pigment is superior in waterproofness to dyestuff. Therefore, the number of opportunities for using pigment as the coloring agent for black ink for a recording apparatus used mainly for outputting documents or the like, has been increasing.
Further, recently, the choice of coloring agent seems to be shifting from dyestuff to pigment, even in the field of color ink.
In the case of pigment-based ink, there are problems which will be described next: When the ink in an ink container is such ink that contains pigment as a coloring agent, and liquid medium in which the pigment is dispersed, and the ink container is left undisturbed for a long period of time, pigment settles, because pigment is greater in molecular weight than dyestuff or the like, being therefore affected by gravity. As a result, the coloring agent concentration within the ink container becomes nonuniform. Here, settle means the phenomenon that microscopic particles are caused to sink by gravity. Provided that microscopic particles do not agglomerate, the rate at which microscopic particles settle is determined by the relation between the speed at which the particles settle in the gravity direction, and which can be obtained by Stokes equation given below, and the Brownian movement of the particles.
Stokesxe2x80x2 equation:
Vs=2a(xcfx81xe2x88x92xcfx810)g/9xe2x80x83xe2x80x83(1)
Vs: setting speed
a: particle radius
xcfx81: particle concentration
xcfx810: solvent
g: gravitational acceleration
: solvent viscosity
Brownian movement:
X=(Rtt/3xcfx80NAxcfx81a)xe2x80x83xe2x80x83(2)
X: average distance particles move in time t
R: gas constant
T: absolute temperature
NA: Avogadro s number
: solvent viscosity
a: particle radius
The microscopic particles settle when the setting speed obtained by the Stokes equation given above overwhelms the dispersion resulting from the Brownian movement.
Further, an ink container is provided with an air vent for connecting the internal space of the ink container to the atmospheric air; allowing the evaporative components in the ink in the ink container to evaporate through the air vent. Therefore, as time goes by, the coloring agent concentration increases, adding to the nonuniformity of the coloring agent concentration in the ink container. In particular, when an air vent is in a surface other than the surface opposing the surface in which the ink outlet is present, the increase in the coloring agent concentration in the adjacencies of the ink outlet caused by the coloring agent settlement and ink component evaporation are more apparent.
In the case of an ink container in which pigment-based ink is directly held in a pouch-like internal container, without being absorbed in an absorbent member or the like, and in which negative pressure is generated using a leaf spring or the like, the pigment in the pouch-like internal container can be easily stirred by utilizing the scanning movement of the carriage resulting from a recording operation. Therefore, the above described pigment settlement does not become a serious problem.
However, in the case of an ink container, the entire internal space of which is filled with absorbent material such as foamed polyurethane, PP fibers, or the like, the ink holding force of the absorbent material substantially suppresses the pigment dispersion. Therefore, the pigment distribution in the absorbent material becomes nonuniform while the ink container is left undisturbed. In the case of this type of an ink container, once the pigment distribution becomes nonuniform, it is virtually impossible to instantly re-disperse the coloring agent. For example, if an ink container is left unused, being mounted in an inkjet recording apparatus, for a long period of time, the pigment settles. As a result, the pigment concentration in the ink in the adjacencies of the ink outlet portion located in the bottom wall of the ink container in terms of the gravity direction increases, whereas the pigment concentration in the ink in the top portion of the ink container decreases. If a recording operation is carried out in this condition, a recording head ejects ink with higher pigment concentration in the initial period of the ink consumption, whereas it ejects ink with lower pigment concentration during the latter half of the ink consumption.
FIG. 1 is a schematic drawing for showing the nonuniform pigment distribution resulting from leaving an ink container undisturbed in the printing position, in a printer. In this drawing, the internal space of the ink container is divided into four regions K, L, M, and N, which are different in pigment concentration, for the sake of convenience, although, in reality, pigment concentration gradient is continuous. According to the knowledge of the inventors of the present invention, while an ink container, the initial pigment concentration of the ink in which was 4%, was left undisturbed, in the non-recording position, in other words, while no ink flow occurred in the ink container, the pigment distribution in the ink became nonuniform, effecting the pigment concentration pattern, given in the following table.
If a printing operation is carried out in this condition, an image with a very high level of pigment concentration is formed in the initial stage of the printing, because the ink in the N region is used in the initial stage, whereas in the latter stage of the ink consumption from the ink container, the ink in the K region is consumed, producing an image with a very low level of pigment concentration. Further, if this ink container is left unused for a long period of time after a printing operation with an extremely low duty is carried out using the ink in the N region, that is, the ink used in the initial stage of ink consumption from the ink container in the above described condition, the ink outlet and its adjacencies are filled with the ink with a very high level of pigment concentration, exacerbating the problem that ink solidifies and adheres to the ink outlet and its adjacencies. As a result, it becomes impossible to recover the printing performance by the recovery mechanism in the printer. These two phenomena are big problems to be solved, in consideration of the recent demand regarding print density.
Further, it is customary that an ink container is individually shipped. Thus, while an ink container is left in the same position, during the shipment, or on a store shelf, for a long period of time, a pigment distribution similar to the above described one occurs. In particular, if an ink container is continuously left undisturbed, with its ink ejection direction being parallel to the gravity direction, a problematic phenomenon such as those described above occurs during the usage immediately following the ink container purchase. It is possible to deal with these problems by making regulations that an ink container be placed sideways, or the ink container attitude be changed once a predetermined length of time, while it is shipped, or while it is kept on a store shelf for sale. However, expecting sales personnel to carry out such operations is not realistic.
As a countermeasure for the problems regarding an ink container containing an absorbent member such as those described above, in particular, the problem of pigment settlement, there is Japanese Laid-open Patent Application 2001-030513, for example. This application is intended to make uniform the pigment distribution by placing a plurality of projections in the ink passage connecting an ink container and a head, so that the ink is stirred while it is supplied from the ink container to the head. This application is effective when the bias in the pigment distribution in the ink container is not excessive, but it cannot be said to be a satisfactory countermeasure in the case of an ink container in which pigment distribution became nonuniform while the ink container is kept in a storage, or left unused, for a long period of time.
Japanese Laid-open Patent Applications 2001-260377, and 2001-26378, 2001-260379 (USAA2001026306) disclose ink container technologies, according to which an ink container is provided with a structure for controlling the amount by which pigment settles to the adjacencies of the ink outlet of an ink container. In particular, Japanese Laid-open Patent Application 2001-260378 discloses a structural arrangement in which the coloring agent settlement in pigment-based ink is prevented by placing partitioning walls alternately in the right and left halves, in the adjacencies of the ink outlet. With the provision of this structural arrangement, the size of the space in which pigment settles is reduced, reducing thereby the amount of the change in pigment distribution. Further, as the ink is supplied to a recording head, it is made to detour around the partitioning walls, being thereby stirred. Consequently, the pigment distribution is made uniform.
However, the partitioning walls disposed alternately in the right and left halves of the ink container are extended only halfway to the opposite walls. Therefore, the portion of the ink container, through which the partitioning walls are not extended, in other words, half the ink container, does not benefit from the effects of the partitioning walls. Further, in the case that the size of the ink outlet portion is half the size of the ink container, the stirring effect created by the presence of the partitioning walls and the ink flow resulting from the ink delivery from the ink container is not fully enjoyed by the ink in the portions of the ink container free of the partitioning wall.
The present invention was made in consideration of the problems of the above described prior art, which must be solved, and its primary object is to control the pigment settlement in pigment-based ink, so that it becomes possible to provide an ink container, which can be employed by an inkjet recording apparatus to produce high quality images.
The present invention for accomplishing the above object is characterized in that an ink container comprising: a negative pressure generating member holding portion containing a negative pressure generating member in which the pigment-based ink to be supplied to an inkjet head is filled; and an ink outlet for supplying the ink to the inkjet head; an air vent for connecting the negative pressure generating member holding portion to the ambient air, further comprises: a single or plurality of ink blocking portions, wherein the ink blocking portions are extended in a manner to block the direct path for the ink to flow to the ink outlet, and also in a manner to partially partition the negative pressure generating member, and wherein the adjacent two sections of the negative pressure generating member created by the ink blocking members are connected to each other through a passage, and each of the ink blocking portions occupies no less than 50% of the cross sectional area of the ink container, at a plane perpendicular to the direct ink path to the ink outlet.
Further, an ink container comprising: a negative pressure generating member holding portion containing a negative pressure generating member in which the pigment-based ink to be supplied to an inkjet head is filled; and an ink outlet for supplying the ink to the inkjet head; and an air vent, which is connecting the negative pressure generating member holding portion to the ambient air, and is attached to the portion which will be at the bottom in terms of the gravity direction, when it is in use, further comprises: a single or plurality of ink blocking plates with an ink passage, wherein the ink blocking plates are extended in the direction perpendicular to the gravity direction, in a manner to partition the negative pressure generating member, and each of the ink blocking portions occupies no less than 50% of the cross sectional area of the ink container, at a plane perpendicular to the gravity direction.
The negative pressure generating member holding chamber for holding the negative pressure generating member is divided into a plurality of blocks by the single or plurality of portions impermeable to ink, or blocking plates. Therefore, the height of each block of the negative pressure generating member in the ink container is lower than that of the negative pressure generating member which has not been divided by the portions impermeable to ink or blocking plates. Therefore, the difference in the pigment concentration, which is created between the top and bottom portions of the negative pressure generating member in an ink container, in which pigment-based ink is contained, by pigment settlement which occurs when the ink container is left undisturbed for a long period of time, is smaller.
The negative pressure generating member may be a single-piece member in which the adjacent two of a plurality of virtually discrete blocks, which will be created by the portions impermeable to ink, or blocking plates, are continuous through an ink passage portion. This structural arrangement assures the ink supply to an inkjet; ink flow is not interrupted at the passage between the two blocks, because the passage section of the negative pressure generating member is continuous with the adjacent two blocks. Further, the negative pressure generating member may be made up of a plurality of discrete smaller negative pressure generating members separated from the adjacent negative pressure generating members by portions impermeable to ink, or blocking plates. In this case, it is desired that a structural arrangement is made so that the closer to the passage, the higher the capillary force of the negative pressure generating member, because such an arrangement ensures the continuous ink flow through the passage.
In the case that a plurality of portions impermeable to ink, or ink blocking plates, are disposed in an ink container, it is desired that a structural arrangement is made so that the projections of the ink passage portions of the negative pressure generating member, that is, the portions of the negative pressure generating member left unblocked by the portions impermeable to ink, or blocking plates, onto a plane perpendicular to the ink delivery direction or gravity direction, do not coincide. In this case, if the negative pressure generating member holding chamber are vertically divided into, for example, three sections, by two portions impermeable to ink, or two blocking plates, the pressure head in the ink passage portion between the middle and bottom negative pressure generating member holding chambers is equal to the pressure head generated only by the negative pressure generating member section in the middle negative pressure generating member holding chamber; in other words, the pressure head of the negative pressure generating member section in the top negative pressure generating member holding chamber does not apply to the ink passage portion between the middle and bottom negative pressure generating member holding chambers. Therefore, the difference in pigment concentration between the top and bottom portions of the portion of the negative pressure generating member corresponding to this passage is smaller by the amount equivalent to the reduced amount of the pressure head.
Further, a portion impermeable to ink, or a blocking plate, may be perpendicular to, or inclined a predetermined angle relative to, the ink delivery direction or gravity direction.
The present invention is applicable to an ink container which is separable from an inkjet head, and is exchangeable by a user, as well as a cartridge integrally comprising an ink container and an inkjet head, which is obvious.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.